Lumber saw mills conventionally employ band saws or circular saws in gangs for cutting logs into rough lumber and in each instance blade guides have been developed to improve the precision of cut. The present invention is concerned with an improved saw balde guide and, as disclosed, is particularly intended for use with circular saw blades, but need not be so limited. Adaptability of the guide, proposed herein for circular saws for use with other types of cutting blades will be obvious to those skilled in the art.
The cutting performance of circular saws has been substantially improved in recent years due to splined arbors, improved wear resistance of the saw teeth, and most important, due to guiding the saws. On the average, kerf reductions of more than 0.070 in. have been achieved in many of the progresive mills and sawing accuracy can be expected to be improved by at least 0.020 in. In addition, surface roughness has been reduced significantly.
With the exception of one recently introduced guide system--known as Flotex.TM. guide--all guide systems involve one pair of guide blocks. The use of two or three pairs at various locations around the saw blade has been studied theoretically and was found to substantially improve the stability of the saw blade. But the application of several guide pairs generally fail due to the fact that mounting of all guide blocks is stationary and rigid. It is not surprising that double or triple or even large guide plates covering up to half the blade failed. The alignment of these guide systems has to be very precise and the required pecision can not be achieved or maintained in sawmill operations. To obtain the benefits of a double guide system --which is much reduced vibration and, in turn, a much smoother cut--a Swedish company introduced the Flotex.TM. guide system mentioned earlier.
The Flotex.TM. system uses two pairs of guides one being a standard guide pair placed in a stationary position below the cut and the other a freely floating guide pair on the back guide of the saw blade below the work piece. The stationary guide controls the position of the saw blade and sawing deviations, and the floating guide functions as a vibration dampener with the result that the non-cutting side of the saw blade in contact with the work piece does not increase kerf or surface roughness. The increase in surface roughness due to contact on the non-cutting side is a more common problem, particularly in the thinner saws.
Saw blade guides can be fixed in position, or they can be mounted to float laterally as has been disclosed in German Pat. No. 3,419,220, published Nov. 29, 1984.
A principal disadvantage to fixedly located guides is that the alignment must be very precise and the required precision cannot normally be achieved or maintained in saw mill day-to-day operations. The floating guide block as in the Flotex.TM. system imposes substantial lateral forces on the saw blade to the extent that it precludes the use of or at the very minimum is unsatisfactory for use with thin blades. Also, because of the mass involved the recovery time is long. The floating guide block works satisfactorily with thick saw blades but are considered unsatisfactory with thin saw blades. To give an indication of what is meant "thin saw blades" have a thickness generally in the range of 0.04 inches to 0.070 inches and have a kerf of roughly 0.08 inches to 0.120 inches. These thin saw blades require less power than the conventional thicker blade, but they can be more susceptible to vibration and deflection during cutting and thus can result in rougher cuts.